Tunas' Diet Has Plenty Of Variety

Bluefins, Yellowfins Eat 4,000 Items Each

May 24, 1992|By SKIP MILLER Daily Press

Cigarette wrappers, monofilament fishing line, plastic bags, seaweed, bits of shells, gravel, 21 different species of fish, sea horses, squid, crabs, and tiny American lobsters were some of the things Charles Barr found during his two-year study of the feeding habits of yellowfin and bluefin tunas.

Barr conducted his study in 1988-89, while he was a graduate student at the Virginia Institute of Marine Science. He inspected the stomach contents of 220 bluefin and 259 yellowfin tunas. He also interviewed charter boat captains and mates on where and when the fish were caught.

The average bluefin he inspected was 24 pounds and 38 inches long. Yellowfins averaged 33 pounds. All the fish were caught off the Virginia coast, from southeast of Virginia Beach's Rudee Inlet to the Eastern Shore.

``Basically, I was putting together all these clues to find out more about the fish,'' said Barr, who is now Marine Science Educator at the Mathematics and Science Center in Richmond.

The smallest tuna he inspected weighed 1 pound and was less than 6 months old.

Tunas are highly migratory species that never rest. Because they have no air bladder, they are heavier than water. If they stop swimming, they sink to the bottom. They swim from birth to death, following water temperatures and available food supply. One bluefin tuna was tagged and recaptured 50 days later, 5,000 miles away.

The main food for both tunas was the sand eel or sand lance, a slow fish that feeds by filtering microorganisms out of water.

Some of the other fish that became tuna delights were needle fish, monkfish, herring, flying fish, butter fish, cutlass fish, file fish, look downs, mackerels, bigeye snappers, butterfly fish and puffers. Short-fin squids were a large part of the yellowfin diet. Sea horses and different kinds of crabs were found in the stomachs of both species. But it was the presence of lobsters that amazed Barr.

``Not the spiny lobsters associated with southern waters but the American, or Maine lobster,'' Barr said.

The yellowfins contained bits of seaweed and other floating debris. The bluefins contained sand and gravel. That led Barr to conclude yellowfins feed at or near the surface, bluefins at or near the bottom.

Al Paschall, a Virginia Beach charter boat captain who has fished for bluefin tuna since 1974, disagreed. ``Bluefins will feed from the top to the bottom, wherever they find food,'' he said.

Paschall said Virginia's bluefin season traditionally begins the first or second week of June. How long it lasts depends on ``how fast the water warms and how fast they eat up the food supply.''

Bluefins are found around a series of mounts and knolls located 15-30 miles off the Virginia coast. To catch yellowfins, boats have to travel 60 miles offshore to the Gulf Stream.

The size of fish caught off Virginia depend on spawning success of previous years, he said. ``If history is any teacher, there will be fish here this year but no small ones.''

If proposed National Marine Fisheries Service regulations are adopted, the daily limit on fish weighing between 14-66 pounds will be one per boat. ``That 66-pound fish is going to make criminals out of all of us,'' Paschall said. ``It's almost impossible to tell the difference between a 70-pound fish and a 65-pound fish until you get them back to the dock and weigh them.''